In the related art, in a circulating type ink supply system applied to an ink jet printing apparatus, positional relationships between nozzles and a liquid level of an upstream pressure source and a liquid level of a downstream pressure source are set. The liquid level of the upstream pressure source is set to a position higher than the nozzles. The liquid level of the downstream pressure source is set to a position lower than the nozzles. The circulating type ink supply system circulates ink according to the level difference between the upstream pressure source and the downstream pressure source. The circulating type ink supply system is needed to maintain the pressure applied to ink in the vicinity of nozzle openings adequately.
In the circulating type ink supply system, it is necessary to select the positions of the upstream pressure source and the downstream pressure source so as to maintain the ink pressure at a nozzle position both during circulation and when the circulation is stopped adequately. Consequently, the physical arrangement of the upstream pressure source and the downstream pressure source in the ink jet printing apparatus is difficult. In the circulating type ink supply system, the length of tubes which connect the upstream pressure source with the nozzles and the downstream pressure source with the nozzles is increased, so that the ink pressure at the nozzle position is instable. In addition, there is a problem such as upsizing of the circulating type ink supply system.
The invention provides a circulating type ink supply system in which the pressure applies to ink in the vicinity of nozzle openings is adequately maintained.